The card below explaining more detail about Gneiss is to be used as cache 4 in this activity. Each of
these caches must be hidden in the ordered labeled from 5-1 to correctly identify this rock.
GNEISS
What type of rock is it? Metamorphic
What minerals make up the rock? Gneiss is usually light in color, but it can be quite dark. It
looks like it has ribbons or stripes of minerals running through the rock. The grain size is usually
fairly coarse. Gneiss usually breaks into blocky pieces, not along the layers. Unlike granite, in
which the crystals are randomly arranged, the crystals in gneiss are lined up and in layers.
Gneiss is a tough and hard rock.
What does it look like? Almost always: feldspar, quartz, and mica.
How was it formed? Gneiss is formed from another metamorphic rock, called schist. The
schist formed from fine grained sedimentary rock (often a shale). Gneiss can be formed also
from some igneous rocks, especially granite. It is usually formed under great pressure from
moving plates of the earth’s crust.
Compare to: granite, schist
Cache 1: Is the rock made of crystal grains? (Does it have a lot of flat, shiny
faces – maybe tiny to small – that reflect light like little mirrors?)
Yes, The rock is made of crystal grains with flat shiny surfaces….
Go to
No There are no (or not many) shiny, flat, crystal grains….
Go to
Cache 2: Does the rock have both layers and crystal grains? (Look carefully for
layers, especially along the edges of the rock.)
Yes, The rock has both layers and crystals…..
No The rock has crystals, but it has no layers…
Go to
Go to
Cache 3: Do the layers look like ribbons or bands of minerals running through
the rock; and is the rock kind of blocky? (The bands of minerals may be straight
or wavy. The rock breaks into blocky chunks, not along its layers.)
Yes, The rock has crystals, layers that look like ribbons or bands of
minerals running through it, and is kind of blocky. It is….
No The rock has crystals and layers that are thin and do not look like
ribbons of minerals. It breaks along the layers. It is…. Go to